struct ListNode* removeElements(struct ListNode* head, int val)
{
    struct ListNode* cur = head;
    struct ListNode* pre = NULL;
    while (cur)
    {
        if (cur->val == val)
        {
            if (cur == head)
            {
                head = cur->next;
                free(cur);
                cur = head;
            }
            else
            {
                pre->next = cur->next;
                free(cur);
                cur = pre->next;
            }
        }
        else
        {
            pre = cur;
            cur = cur->next;
        }
    }

    return head;
}